In conventional heap and dump leaching of copper sulphide containing minerals, mined ore is stacked into heaps, aerated through direct injection of air via aeration pipes extending into the heap and/or by natural convection through exposed sides of the heap, irrigated with an acid solution for extraction of copper into solution, and the copper is subsequently recovered from solution by a range of recovery options including solvent extraction and electrowinning (SX/EW), cementation onto more active metals such as iron, hydrogen reduction, and direct electrowinning. Leaching may be enhanced by the use of microorganisms, such as acidophilic bacteria that grow on the surface and in the cracks of ore fragments in a heap.
Generally, heap and dump leaching (hereinafter referred to as “heap leaching”) provides lower metal recoveries than other metallurgical process options for recovering copper from copper-containing ores, such as milling and flotation that produces copper-containing concentrates that are then smelted to produce copper metal. Consequently, heap leaching tends to be reserved for low grade ore types (typically, 0.5-2 wt. %) that have at least a proportion of readily recovered copper, but where crushing/milling costs per unit of copper are too high to support a concentrator approach, or where mineral liberation and other characteristics (e.g. arsenic content) will not support production of directly useable or saleable concentrates.
The above description is not to be taken as an admission of the common general knowledge in Australia or elsewhere.